treatment of the data. Since preliminary graphs indicated that the most pronounced deviation occurs in solvents with G values greater than 80 (benzene), two lines were generated using benzene as the breaking point. The results for tert-butylamine at 6% and 0.16% (Figure 6, E and F ) and for cyclohexylamine at 6% (Figure 6 A ) illustrate correlation of G to absorbance on a single slope throughout the range of solvents investigated, with some scatter of points occurring above G = 80. Deviation from initial slope becomes more pronounced, and generation of a second slope is noted in Figure 6B for cyclohexylamine determined at 0.16% concentration and in Figure 6C and 6D for n-butylamine a t both the 6% and 0.16% concentrations. Deviation from initial slope in these systems is postulated to occur a t the point where H-bonding of the solvent to amine is sufficient to interfere with the N-H..N bond of solute to solute. The fact that the slope after this point is less than the initial slope is in agreement with this postulation (more H-bonding is present than would be predicted by extrapolation of the initial slope). For each amine-amine bond that the solvent disrupts, two amine-solvent bonds will form in its place, resulting in greater absorbance of the H-bonded 2.02-pm band. It can also be seen from Figure 6 that different amines and the same amine a t different concentrations show differences in change of slope. tert-Butylamine in a series of solvents at both 6% and 0.16% concentrations shows no deviation from initial slope, while n-butylamine has a definite change in slope in both series. Cyclohexylamine, however, shows no deviation in slope in the 6% series but a definite slope change in the 0.16% series. These differences can be explained in terms of amine structure (relative Taft +cr* values). An amine such as tert-butylamine whose structure allows strong amine to amine H-bonding would be less affected by solvent to amine H-bonding and thus would not show a change in slope with increasing solvent H-bonding potential (G value). For weak amine to amine H-bonds such as in n-butylamine, the solvent even in concentrated amine solution can easily replace the amine to amine attraction. A marked change in slope would result at the point where solvent H-bonding overtakes amine to amine H-bonding. For a compound of intermediate amine to amine H-bond strength, cyclohexylamine, such bonding is vulnerable to solvent H-bonding only in dilute solution. A change in slope would again occur where solvent-amine attraction becomes stronger than amine-amine attraction. However, this effect would be less noticeable in concentrated solutions where the percentage of amine to amine attractions increases.
!lor v)
IO0
2 9W
C 80 70[
> 60
D.
n
(,,,/05
- butylamine , , , 6%,
!
1
:-butylamine
B/,,
0.l6Y;
40
I-
70
a
50
t -butylamine 6% .2
.3
.4
.5
.6
.7
.8
002
006
010
014
018
022
ABSORBANCE ot 2 02 p m
Figure 6. Correlation of solvent-solute values) to absorbance at 2.02 pm
hydrogen bonding (G
Solvents: A , hexane; 6 ,cyclohexane; C. dibutyl ether; D , triethylamine: E , diethyl ether: F , tetrachloroethylene; G, carbon tetrachloride; H , toluene; I , benzene; J , dioxane; K , acetonitrile: L . pyridine: M . 1,2-dichloroethane; N. nitromethane; 0 , dichloromethane; P , chloroform; and R , dibromomethane
Thus, these solvent effects reemphasize the interplay of solvent, concentration, and structure in H-bond studies involving the combination bands of primary aliphatic amines.
ACKNOWLEDGMENT The authors thank Gary Crabill, Computer Center, Purdue University at Fort Wayne, for the least squares calculation of data. Received for review December 14, 1971. Resubmitted April 13,1973. Accepted August 2,1973.
CORRECTION Rapid Determination of Barbiturates by Gas Chromatography- Mass Spectrometry In the paper by R. F. Skinner, E. G. Gallaher, and D. B. Predmore [Anal. Chem., 45, 574 (1973)], the following sentence starting on line 5, column 2, page 574, and following references should be added. ". . . .for GC-MS identification. Similar extraction-methylation procedures for a number Of drugs barbiturates have been presented in the literature (11-17)."
(11) E. J. Gallaher and R. F. Skinner, Proc. N.W. Regional Meeting, ACS, Paper No. 43 (1970). Anal. Chem.9 42,421 (1970). (12) J. (13) E. B. Solow and J. B. Green, Clin. Chirn. Acta., 33,87 (1971). (14) J. MacGee, clin. Chern., 17, 587 (1971). (15) E. B. SOIOWand J. B. Green, Neurology, 22,540(1970). (16) G. Kananen, R. Osiewicz. and I . Sunshine, J. Chrornatogr. Sci., 10, 283 (1972). (17) R. F. Skinner, E. J. Gallaher, J. 6. Knight, and E. J. Bonelli, J. ForensicSci., 17,189 (1972).
A N A L Y T I C A L CHEMISTRY, VOL.
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